PSYCH 261 Test 3 - Touch and Pain

somatosensation includes…

exteroception, interoception, and proprioception

exteroception

sensation from skin provides information about external world

interoception

sensation from internal organs provides information about internal functions

proprioception

sensation from muscles and tendons to convey body position and movement

low-threshold mechanoreceptors (LTMRs)

touch receptors

includes the epidermis, dermis, and subcutis

epidermis

glabrous (hairless) skin

dermis includes…

merkel disk, ruffini endings, meissner corpuscle, and pacinian corpuscle

merkel disks

skin type: glabrous and hairy

physiological subtype: slowly adapting type 1

continued firing while stimulated

optimal stimulus sensitivity: continuous pressure, very low-frequency vibration

axon type: AB fibers

ruffini endings

skin type: glabrous and hairy

physiological subtype: slowly adapting type 2

continued firing while stimulated

optimal stimulus sensitivity: continuous pressure, skin stretch

axon type: AB fibers

meissner corpuscles

skin type: glabrous

physiological subtype: rapidly adapting type 1

rapid response, stops signaling when new state occurs, fires again when stimulus changes

optimal stimulus sensitivity: changes in pressure, low-frequency vibration

axon type: AB fibers

pacinian corpuscles

skin type: glabrous and hairy

physiological subtype: rapidly adapting type 2

rapid response, stops signaling when new state occurs, fires again when stimulus changes

optimal stimulus sensitivity: changes in pressure, high-frequency vibration

axon type: AB fibers

simultaneous two-point discrimination task

single stimulus presented on 25% of trials and two stimuli presented on 75% of trials

see if someone can discriminate if one or two is touching the back of the hand

discrimination threshold

the distance between two stimuli at which people are just able to tell they are being touched by two stimuli rather than one stimulus

small threshold = less receptors

high threshold = more receptors

high-threshold mechanoreceptors (HTMRs)

pain receptors

includes c fibers, alpha-delta fibers, and alpha-beta fibers

free nerve endings from these connect up to the epidermis

how mechanoreceptors translate touch

stretch activation, activation by tethers, and indirect activation

stretch activation

an ion channel is pulled open when you stretch it

activation by tethers

when something moves outside it, it tugs on the tether and opens the ion channel

indirect activation

a membrane bound protein beside the receptors causes it to open

heat transduction

transient receptor potential vanilloid 1 (TRPV1) ion channel is exposed to heat changes

the configuration allows the ion channel to open and allow positive ions in

they are also ligand activated - something will bind to it and cause it to open

polymodal - respond to both temperature and a ligand

capsaicin

present in spicy food

stimulates a temperature change and causes the receptor to open

cold transduction

transient receptor potential member 8 (TRPM8) ion channel responds to cold stimulation and opens the receptor

also activated by menthol (ligand) that causes the receptor to open

polymodal because it responds to both temperature and a ligand

what happens when something it too hot for the skin?

burns the skin and destroys receptors

severe burns lose sensitivity in TRP receptors

dermtome

the region of skin serviced by a single spinal nerve

where you perceive it and where it goes to the spinal cord

alpha-beta fibers from low-threshold mechanoreceptors go…

through the dorsal root ganglion and up the ipsilateral dorsal-column medial-lemniscus (touch)

pain and temperature information goes…

through the dorsal root ganglion to the contralateral side and up the spine on the spinothalamic tract

touch and pain in the medulla

dorsal column-medial lemniscus crosses over to the contralateral side here

spinothalamic tract continues up on the contralateral side

touch and pain in the midbrain

spinothalamic tract and dorsal column-medial lemniscus continue towards the brain on the contralateral side

spinothalamic tract

touch and pain in the brain

on the contralateral side of the brain

passes through the ventral posterior nucleus (VPN) of the thalamus

ventral posterior nucleus (VPN) of the thalamus

where touch and pain is processed

section 1 of secondary somatosensory cortex

responsible for coding texture of objects and pain

in the postcentral gyrus

section 2 of secondary somatosensory cortex

responsible for coding size and shape of objects

section 3a of secondary somatosensory cortex

responds to movement of joints, tendons, and muscles, as well as some types of pain inside the body

section 3b of secondary somatosensory cortex

responds to size, shape and texture of objects, as well as pain

parietal lobe

where is the primary and secondary somatosensory cortex?

emotional evaluation of pain

activates the intralaminar nuclei of the thalamus as well as the amygdala, hippocampus, prefrontal cortex, and cingulate cortex

feelings of pain, memories of pain and cues associated with pain activates the somatosensory cortex (via the VPN)

pain relief

opiate receptors are occupied by the endorphins

endorphin release reduces the release of substance p and inhibits the signal of the pain

placebo

a drug or other procedure with no pharmalogical effect

reduces pain responses in the brain and in the spinal cord

cannabinoids

block pain in the periphery of the body as well as the central nervous system